1. Field of the Invention
This invention relates to an image forming apparatus such as a transfer type electrophotographic apparatus or a transfer type electrostatic recording apparatus in which an image forming process is applied to an image bearing member such as an electrophotographic photosensitive member or an electrostatic recording dielectric member to thereby execute image formation and the image bearing member is repetitively used for image formation.
2. Related Background Art
A description will hereinafter be made of a transfer type electrophotographic apparatus (a copying apparatus, a printer or the like) as an example.
The transfer type electrophotographic apparatus generally uses as an image bearing member a rotatable drum type electrophotographic photosensitive member (a photosensitive drum) provided with a photosensitive layer as an image making layer on the outer peripheral surface of an electrically conductive drum base body, and applies known suitable image forming processes such as charging, image exposure and development thereto to thereby form a toner image corresponding to desired image information. The toner image is transferred to a transfer sheet as a recording medium by transfer means, and the transfer sheet to which the toner image has been transferred is separated from the surface of the photosensitive drum, and the toner image is fixated as a permanently secured image by fixating means, and the transfer sheet is discharged as an image forming article. Also, after the separation of the transfer sheet, the surface of the photosensitive drum has any residual contaminant such as untransferred toner (residual toner) thereon removed by cleaning means and is thus cleaned for repetitive use for image formation.
Also in such an image forming apparatus, an apparatus construction of the process cartridge mounting and dismounting type is widely used for a compact copying apparatus, a printer or the like in order to facilitate the maintenance of the apparatus. This is an apparatus construction in which process instruments such as a photosensitive drum as an image bearing member, a charging member for uniformly charging the photosensitive drum, developing means and cleaning means are made into a process cartridge contained as an unit and collectively removably mountable with respect to a main body of the image forming apparatus, and when the instruments therein reach their life, the entire process cartridge is replaced with a new one.
The photosensitive drum has a predetermined life and in some cases, it is interchanged by a serviceman judging the life from the integrated print sheet number value of a print sheet number counter provided on the apparatus body, but many photosensitive drums are set so as to be interchangeable by a user to enhance the convenience to the user. In this case, there is means for counting the number of rotations of the photosensitive drum to inform the user of the interchange time for the cartridge. As shown in Japanese Laid-Open Patent Application No. 6-266270, there is disclosed a method of detecting the quantity of waste toner in the waste toner container of a cleaning device to thereby cause that quantity to be displayed on the apparatus body.
1) However, for example, when the life of the photosensitive drum is reached and the process cartridge has reached the end of its life, if all of image forming operations are stopped to prevent a bad image or the overflow of waste toner, fax reception particularly at night or during absence becomes impossible in the case of an image forming apparatus having the fax function. As a countermeasure for it, there is usually adopted a method of providing a memory and temporarily accumulating received data therein, but the amount of data accumulated in the memory is limited and any amount exceeding the limit cannot be received. Also, if the memory is increased, this problem will be somewhat improved, but the cost of the apparatus will increase.
2) In the case of an image forming apparatus having the printing function of printing computer output data, if display is effected only on the image forming apparatus side even when the life of the process cartridge is nearly over, the user of the computer will be late in becoming aware of it.
There have also been the following problems.
3) Even when the life of the photosensitive drum is over and the process cartridge has reached its life and the acceleration of the interchange of the process cartridge is displayed, a new process cartridge is often not prepared beforehand, and therefore in some cases, a process cartridge having reached the end of its life had to be intactly used even if a bad image such as an injury or fog had occurred, or the use of the image forming apparatus had to be stopped.
4) The photosensitive layer of the image bearing member is gradually scraped by the image forming operation being repeated. The life of the process cartridge, i.e., the life of the image bearing member, is prescribed by the remaining film thickness of the photosensitive layer.
As a method of detecting the life of the process cartridge, there is also known a method of judging it from the number of outputted image sheets, but the remaining film thickness of the photosensitive layer by which the life of the image bearing member is prescribed differs depending on the size of the outputted sheets, or the condition as to whether the sheets have been outputted one by one or have been continuously outputted and therefore, there arises the problem that a bad image occurs before output is done from life detecting means or conversely, output is done from the life detecting means before a bad image occurs.
5) If the user continues to use the image forming apparatus in spite of the process cartridge having reached the end of its life and display for the acceleration of the interchange of the process cartridge being done, the waste toner container of the cleaning means becomes full of waste toner, which overflows from the cleaning means and contaminates the interior of the apparatus and further stains the printing sheet.
6) Even if it becomes known on the basis of the output from means for detecting the film thickness of the photosensitive layer of the image bearing member that the life of the process cartridge is nearly over or has been reached, if much time is required before a new process card is obtained when there is not prepared a new process cartridge beforehand or if the time from after the display of the life till the occurrence of a bad image is short, there will arise a problem similar to that noted under item 4) or 5) above.
7) If a developing bias or a transfer bias is applied during the detection of the film thickness of the image bearing member, the electric current thereof will flow into the film thickness detecting means, and therefore the detection error will become great.
The problems as noted above are matters not restricted to image forming apparatuses using a process cartridge including an image bearing member, but common to image forming apparatuses which do not use a process cartridge and in which the image forming process is applied to an image bearing member to thereby execute image formation and the image bearing member is repetitively used for image formation.